Many hydrocarbon wells are produced by electrical submersible well pump assemblies (ESP). A typical ESP includes a centrifugal pomp having a large number of stages, each stage having an impeller and a diffuser. An electrical motor couples to the pump for rotating the impellers. A pressure equalizer or seal section connects to the motor to reduce a pressure differential between lubricant in the motor and the hydrostatic pressure of the well fluid. The pressure equalizer has a motor lubricant passage leading from a flexible barrier such as a bag or bellows into the Interior of the motor. The motor lubricant passage is always open to communicate well fluid pressure applied in the pressure equalizer to the flexible barrier to the motor lubricant in the motor.
With most prior art ESP's, the pressure equalizer or seal section is located between the motor and the pump. In others, the pressure equalizer is mounted below the motor. The pressure equalizer may comprise an upper and lower pressure equalizer in tandem. An intermediate connection between the upper and lower pressure equalizers has an intermediate motor lubricant passage for communicating motor lubricant between the flexible elements in each.